Recently, in the field of magnetic recording, demand for higher density has been increased and development has been made to meet such demand. With the increase of the density, several types of heads for hard disks have been studied and developed, such as a thin-film magnetic head in which a soft magnetic thin film is used as magnetic poles.
There are different types of thin-film magnetic head, including MR head, GMR head, and TMR type or CPP type head.
Typically, the thin-film head adopts the CSS (Contact Start Stop) type in which the thin-film head is floated above the recording medium by bearing effect of air. The head is generally held at a distance (about 1-10 nm) slightly above the magnetic disc rotating at a high speed. Therefore, surface strength and abrasion resistance, that provide tolerance to head crash and CSS abrasion, are important. Various studies have been made to improve the abrasion resistance, as disclosed, for example, in Japanese Patent Application Kokai No. 4-276,367, in which a protective film is formed on a rail of a magnetic head slider. This protective film consists of a silicon layer having a thickness of 250 Å (25 nm) or less, exhibiting low strength. In addition, when such a silicon layer is applied to the magnetic thin-film head structure containing a sintered substrate made of alumina and titanium carbide, an alumina insulation layer, a thin film made of a soft magnetic material (e.g. permalloy, Sendust, iron nitride and the like) and the like, cohesion or adhesiveness between the thin-film head and the protective film becomes poor, leading to problems such as peeling of the film and insufficient abrasion resistance.
For protective layer to improve the abrasion resistance, thin-film made of TiN or TiCN, diamond-like carbonaceous film (DLC) and the like have been known. However, use of these films on the thin-film magnetic head cannot attain sufficient durability.
Japanese Patent No. 2,571,957 discloses that a buffer layer consisting of amorphous silicon and amorphous silicon carbide is formed on the surface of an oxide, and then a film of carbon or a film mainly composed of carbon is further formed thereon. However, even though the protective layer with the buffer layer is applied to the thin-film head, sufficient durability cannot be attained. In addition, it has disadvantages in that the extra step is required to form the buffer layer, in addition to the step to form the protective film, leading to a longer production period and a higher production cost. Moreover, the buffer layer makes the film thicker, which contradicts the demands on the magnetic head for hard disk, such as cost-effectiveness, mass-productivity, and larger packing density.
Under these circumstances, the present applicant has proposed an Si—C protective film formed by vapor deposition from predetermined compositions (see Japanese Patent Application Kokai Nos. 10-289419 and 10-275308).
The storage capacity of hard disc depends on the performance of the head, and the future market will demand the capacity of 120 GB or more. Therefore, the thickness of the protective film covering the head is demanded to be 3 nm (30 Å) or less.
On the other hand, the above-disclosed protective film realizes a thickness of approximately 7 nm (70 Å), due to the limitation in the technical level at that time, and thus sufficient durability cannot be obtained if the film is used as it is. Especially, corrosion resistance against water is important, since the problem of water condensation may occur in the device.